1. Field of Invention
The present invention generally relates to a method for finishing a plastic concrete mixture. More particularly, the present invention relates to a method for introducing and consolidating a dry shake aggregate additive into plastic concrete mixtures using a vibrational finishing tool.
2. Description of the Prior Art
In constructing concrete structures, such as concrete slabs and the like, certain conventional procedures involve placing a plastic concrete mass inside of a form and finishing the top surface in various well known manners and permitting the concrete to harden with no vibration of the concrete mass whatsoever. Other procedures involve the use of vibrators placed temporarily into or upon the concrete mass at various locations, with the surface being finished by using various combinations of striking off the surface and/or troweling operations, including the use of hand trowels, powered rotary trowels and the like. It is also generally known that, if not worked, the surface of wet concrete would take on a highly undesirable rough and uneven finish which, after partial setting of the concrete, would render the surface difficult if not impossible to finish to the desired smooth and even consistency.
The conventional process for pouring and finishing concrete is labor intensive and consists of the steps of:
1. Pouring fresh concrete into forms.
2. Screeding or striking off the concrete to preliminarily level the surface of the concrete.
3. Tamping the concrete i.e., with a bull float or similar device to bring the finer aggregates to the surface.
4. Applying a xe2x80x9cdry shakexe2x80x9d aggregate to harden and/or color the concrete.
5. Moving a bull float over the surface of the wet concrete to mix the xe2x80x9cdry shakexe2x80x9d with the upper layer of the concrete.
6. Moving another rectangular tool such as a hand trowel or fresno, over the bull floated concrete.
7. Allowing the concrete to dry an amount sufficient to support the weight of an individual.
8. Utilizing a power trowel to put a smooth finish on the surface of the concrete.
The above described conventional method of finishing concrete is labor intensive. Accordingly, it would be very desirable to provide an improved method for finishing concrete that would permit concrete to be finished in a substantially shorter period of time. It would also be desirable to provide a method that would permit concrete to be finished with a surface which is very level, and would produce a highly polished surface finish. Therefore, it is a principal object of the invention to provide an improved method and apparatus for finishing freshly poured concrete.
After concrete is initially laid, it must be worked while it is wet in order to provide a smooth, homogeneous mixture. Working the concrete helps settle the concrete and helps densify and compact the concrete during finishing. The working also removes air voids and brings excess water and fine aggregates to the surface for subsequent finishing. After the initial finishing stages are complete, a more detailed work frequently commences, generally by means of a hand-held float to further compact the concrete for purposes including the driving of suspended gravel downwards. This floating help develop a wetted surface slurry or soup-like finish, while further driving out air pockets and the like for preparing the surface for final finishing. A bull float is most often used for this stage of compacting and smoothing the concrete. The bull float is a rectangular piece of material made from pinewood, magnesium or material other than iron or steel. (Iron xe2x80x9csealsxe2x80x9d concrete, which is not desirable during initial floating).
This floating is often accompanied by some sort of vibration of the concrete. In the above-described process, various large vibrating devices may be beneficially employed. Illustrative embodiments of such large vibrating tampers or the like may be seen in U.S. Pat. No. 3,306,174 to Wardell, U.S. Pat. No. 2,289,248 to Davis, U.S. Pat. No. 1,955,101 to Sloan, and U.S. Pat. No. 2,209,965 to Mall. These devices generally include a rather large flat base plate, a heavy and bulky vibratory mechanism disposed thereon, and an elongate handle attached thereto for moving the large plate across the concrete surface. Such devices are generally intended to provide a general smoothing and compacting operation over a large area.
After the concrete is floated, and a slurry forms, the surface of the concrete has a slight water sheen. The water sheen will evaporate from the surface of the concrete, leaving no apparent water sheen on the concrete surface. The speed of evaporation is dependent on ambient conditions such as temperature, humidity and exposure to wind or direct sunlight. It is at this point, i.e., when the water sheen has just disappeared from the concrete surface, that a xe2x80x9cdry shakexe2x80x9d hardener may be applied to the concrete.
In the related art, diverse attempts have been made to control and modify the characteristics including the surface characteristics of concrete flooring, road beds or the like with different types of additives. U.S. Pat. No. 4,746,788, to Shaw et al discloses a process for producing a concrete surface of seeded exposed aggregate using small, rounded aggregate (preferably sand) which is broadcast over the upper surface of the pour and thereafter mixed into the cement paste of the concrete pour matrix. A surface retarder and vapor barrier is applied for a short-term (approximately 4 to 24 hours) and removed and the concrete is thereafter cured by fogging or with a soaker hose and, after approximately 30 days, the surface residue is removed with a steam/acid wash to expose the finished floor.
Another method of producing a sand/cement upper surface is disclosed in U.S. Pat. No. 4,281,496, to Danielsson in which larger aggregate is allowed to settle, producing a thin upper layer formed substantially of sanded cement which is thereafter floated to remove surface irregularities. After curing 1 to 5 days, the upper surface is treated in a grinding operation to produce a flat, porous surface having a sanded quality.
Another technique involves the application of an excessively dry top dressing mix while the concrete base is still wet. Water rising from the base concrete penetrates into the topping and the two bond together. The top stratum of the conglomerate can then be wetted and floated to achieve a smooth finish. Such a system is shown by Sloan in U.S. Pat. No. 2,078,289. Reardon, in U.S. Pat. No. 2,853,928, discloses a method for curing concrete in which a dry powder composition is spread over the top of the wet concrete to absorb the excess moisture. The dry powder, however, is not blended into the concrete base and after the concrete is cured for a sufficient length of time, the dry powder is removed by vacuuming or sweeping. That composition is approximately 80 parts silica and about 20 parts salt. It is further known to apply a dry shake into a concrete base to control the concrete surface moisture. The dry shake may be incorporated to produce a monolithic cementitious floor by using various processes.
The American Concrete Institute (ACI) has approved an application procedure (No. 302) for adding a dry shake hardener to concrete. This procedure includes the following steps. Immediately after the slab surface has been floated, the first shake is applied in a uniform application by hand, spreader or other suitable method placing the material on the edges of the slab first. A mechanical spreader gives better results and is highly recommended. The first shake is allowed to remain unworked on the surface until it has absorbed moisture as evidenced by a change to a darker color. Then, it is floated with a hand or power float. Immediately after floating in the first shake, the second shake is applied, again placing the material on the edges of the slab first. The second shake is applied and floated in a like manner.
A problem with prior methods of finishing concrete is that moisture may evaporate quickly from the surface of the concrete such that there is not sufficient moisture to hydrate cementitious aggregates in dry shake hardener.
Another problem associated with prior methods of finishing concrete is that it is difficult to monitor and determine the time when the concrete surface has the optimum moisture content for application of dry shake hardener.
Another problem with prior methods of finishing concrete is that after excess moisture has evaporated from the surface of concrete, that one cannot add water to the surface during the finishing operation, or the surface layer may delaminate.
Another problem with prior methods of finishing concrete is that application of a dry shake hardener too late (i.e., when there is insufficient surface moisture) can cause delamination of the surface layer of the concrete.
Another problem with prior methods of finishing concrete is that application of dry shake hardener too early can cause the aggregates of the hardener to sink into the plastic concrete, causing a porous finish.
Another problem with prior methods of finishing concrete is that early application of dry shake hardener causes delamination, crazing, scaling and dusting on the surface layer of concrete.
Another problem with prior methods of finishing concrete is that during application of dry shake hardener, the hardener or colorant may not be properly mixed into the upper layer of concrete.
Another problem with prior methods of finishing concrete is that improperly applied dry shake hardener can cause uneven color in the concrete.
Another problem with prior methods of finishing concrete is that improperly applied dry shake hardener can cause uneven levels of hardening in the concrete.
Another problem with prior methods of finishing concrete is that bullfloating may not sufficiently consolidate, i.e., mix the dry shake hardener with the surface layer of the concrete.
Another problem with prior methods of finishing concrete is that when a dry shake hardener is not sufficiently consolidated with the surface layer of the concrete, that there is no smooth interface between the surface layer and the remainder of the concrete.
Another problem with prior methods of finishing concrete is that when the interface between the surface layer and the remainder of the concrete is not smooth, then the surface layer may delaminate at that interface.
After the conventional step of bullfloating the dry shake into the surface layer of the concrete, it is conventional to employ a smoothing or finishing trowel to develop a very smooth surface. It is also conventional to employ specialty tools (such as edgers) to provide finishing touches to the work (such as curved edges or the like) and steel trowels to seal the concrete. Flat steel troweling followed by raised steel troweling is used for typical finishing.
Prior methods of smoothing plastic concrete using a hand trowel are not effective in removing water or air pockets that may be trapped in the concrete. A simple hand trowel typically consists of a handle and a flat metal blade. The trowel is used to smooth the top layer of poured concrete, but has little effect on water or air below the surface of the concrete. Conventional hand trowels are also hard to use near walls or corners because they must be wiped back and forth over the surface of the plastic concrete and the wall often is an obstruction. Conventional hand trowels are also difficult to use for long periods of time because of the high amount of friction between the blade of the tool and the concrete.
Illustrative of the other types of finishing tools used at this stage is the power trowel. When the concrete has dried sufficiently to support the weight of an individual, i.e., when an adult can walk in a normal manner on the concrete without having his or her footsteps form depressions in the surface of the concrete, finishing with a power trowel may commence. The blades on a conventional power trowel are generally rotated at over one hundred rpm to overcome the frictional forces generated when the trowel blades move over the relatively dry surface of partially hardened concrete. The power trowel blades ride on and smooth the surface of the concrete and three or four passes of a power trowel over the entire surface of a slab of concrete are ordinarily required to properly finish the concrete. The power trowels ordinarily weigh at least one hundred and twenty pounds.
Alternatively, when the work has progressed to the finishing stage wherein it is desired to provide a highly smoothed surface finish, a variety of prior vibrating hand trowels have been employed with varying degrees of success. Representative examples of such trowels that are primarily for smoothing or finishing work may be seen in U.S. Pat. No. 3,376,798 to Bodine, U.S. Pat. No. 2,514,626 to Clipson, and U.S. Pat. No. 2,411,317 to Day et al. Whereas such trowels are, in contrast to the aforementioned larger devices, intended for hand-held operation, they retain several characteristics of the larger devices such as being of a rather awkward, large and heavy construction. In a hand-held tool this bulk, weight, and complexity may render the tool totally impractical for use, particularly in view of the fact that the operator is typically working for long periods of time on his knees and often in awkward positions.
It must be recognized that these trowels are conventionally used primarily in the finishing operations wherein a great deal of vibratory energy is not required inasmuch as a mere final smoothing of the surface slurry is being effected. Notwithstanding, a variety of such vibrating means have been attempted to be employed including plunger-type vibrators (as disclosed in the patent to Clipson), air driven turbine vibrators (as disclosed in the patent to Day), and even sonic air-driven orbiting-mass type vibrators (as illustrated in the patent to Bodine).
Another prior vibrating hand trowel is disclosed in U.S. Pat. No. 5,234,283 to Adkins. In this trowel the vibratory mechanism is mounted inside the handle. The vibratory mechanism vibrates a rigid metal blade of relatively large mass by xe2x80x9cpushing offxe2x80x9d of the handle in an oscillating fashion. An inherent consequence of this construction is that the handle vibrates as much or more than the blade of the trowel that contacts the wet concrete. These vibrations cause discomfort and difficulty of use for the operator. As a means of reducing the amount of uncomfortable vibrations transmitted through the handle to the operator, this device, in practice, is typically manufactured such that the handle/vibrator mechanism is of relatively high mass. Also, because only one vibrating mechanism (i.e. located in the handle and attached to the blade of the trowel at one point) is used to drive the entire blade, the blade must be constructed of particularly rigid, (and therefore frequently heavy and thick) material in order to cause the entire blade to vibrate in phase. As discussed above with respect to other prior vibrating finishing tools, it is undesirable for such tools to be heavy and bulky. Heavier tools may sink into the concrete causing depressions in the surface because the working surface of the tool applies too much pressure to the concrete surface.
A more desirable finishing tool would incorporate characteristics that would cause the majority of the vibratory energy to be transmitted to the work concrete through the bottom of the device in an efficient and uniform manner and not to the operator through the handle. It is also desirable that the ratio between a finishing tool""s weight and its working surface""s area be low so as not to cause depressions in the surface of the concrete.
A problem with prior methods of finishing concrete with prior finishing tools is that they are not effective in removing water or air pockets that may be trapped in the concrete.
Another problem with prior methods of finishing concrete with prior finishing tools is they are difficult to use for long periods of time because of the high amount of friction between the blade of the tool and the concrete.
Another problem with prior methods of finishing concrete with prior finishing tools is bulk, weight, and complexity may render the tool totally impractical for use.
Another problem with prior methods of finishing concrete with prior finishing tools is the handle vibrates as much or more than the blade of the finishing tool causing discomfort and difficulty of use for the operator.
Another problem with prior methods of finishing concrete with prior vibrational finishing tools is that t he weight of the vibrating mechanism causes the tool to sink into the concrete causing depressions in the surface of the concrete.
Another problem with prior methods of finishing concrete with prior power trowels is the weight of the power trowel increases the wear on the trowel blades.
Another problem with prior methods of finishing concrete with prior finishing devices is the weight of the device creates new depressions in the surface of the concrete.
Another problem with prior methods of finishing concrete with prior finishing tools is that they redistribute the upper layer of the concrete causing xe2x80x9cwavesxe2x80x9d on the surface of the concrete from the alternating depressed and raised areas.
Another problem with prior methods of finishing concrete with prior finishing tools is that lighter tools do not vibrate sufficiently to removes the xe2x80x9cwavesxe2x80x9d in the surface of the concrete.
The present invention generally relates to a method of advantageously finishing an exposed surface of a plastic concrete mass using a dry shake hardener in conjunction with a vibrating finishing tool. The finishing tool together with a dry shake hardener may be used to modify the texture or character (i.e. the xe2x80x9cfinishxe2x80x9d) of a surface of the concrete. A dry shake hardener may be consolidated with a slurry formed on the surface of a plastic concrete mixture more readily when the dry shake hardener is vibrated together with the slurry. The following disclosure also describes the preferred embodiment of the vibrating finishing tool used in that method.
The vibratory action of the finishing tool is generated by one or more piezoelectric actuators which, when energized vibrate at a selected frequency. In the preferred embodiment of the invention, the vibrations are transferred through a blade at the bottom of the finishing tool and into the plastic concrete. This vibration causes air and water to rise to the surface of the concrete creating a layer of moisture on the surface of the concrete. This moisture also advantageously lubricates the working surface of the finishing tool, making for easier use, and creates a slurry which is desirable for producing a smooth surface finish. The moisture is also advantageously absorbed by the dry shake hardener and worked into the upper layer of the concrete. The vibrations are at such a high frequency and the displacement of the bottom surface of the finishing tool is so small that the operator can barely feel the vibrations through the tool""s handle. This, coupled with the lightweight design and other characteristics described herein below, makes the finishing tool very easy to handle and operate.
Accordingly, it is a primary object of the present invention to provide a method of finishing the surface of plastic concrete which includes the step of vibrating the concrete with a vibrating finishing tool.
It is another object of the present invention to provide a lightweight, energy efficient, piezoelectrically actuated vibrating surface finishing tool for the step of vibrating the concrete.
It is another object of the present invention to provide hand-operated concrete/cement working tools of an automatically vibrating variety wherein a substantial vibratory energy is imparted to the concrete surface.
It is another object of the present invention to provide a device that is effective in creating a smooth and wet top layer in the plastic concrete for lubrication of the tool and a smooth finish of the concrete.
It is another object of the present invention to provide a device of the character described in which the piezoelectric element(s) is(are) protected from damage within a sealed interior chamber.
It is another object to provide a modification of the present invention in which the vibratory energy is imparted into the concrete in the frequency range of 50 to 500 hertz.
It is another object to provide a modification of the present invention in which the frequency of vibration is easily user-modified.
It is another object of the present invention to provide a device of the character described that is battery powered.
It is another object of the present invention to provide a device of the character described that makes trapped water and air in a concrete mixture rise to the surface of the concrete.
It is another object of the present invention to provide a method and device of the character described in which released moisture is used to hydrate a dry shake hardener or colorant.
It is another object of the present invention to provide a method and device of the character described that consolidates a dry shake into the surface layer of concrete.
It is another object of the present invention to provide a method and device of the character described that consolidates a dry shake into the surface layer of concrete faster and easier than conventional techniques.
It is another object of the present invention to provide a method and device of the character described in which the surface layer of concrete is smoothed and flattened.
It is another object of the present invention to provide a method and device of the character described in which the surface layer of concrete is smoothed and flattened simultaneously with the consolidation of a dry shake into the concrete.
Further objects and advantages of this invention will become apparent from a consideration of the drawings and ensuing description thereof.